1. Field of the Invention
The present invention relates to hardenable compositions based on prepolymers containing both imide and siloxane groups and various adjuvants, and, more especially, to thermosetting such compositions which are storage-stable, film-forming at temperatures of from 40.degree. to 90.degree. C., adhesive at ambient temperature and also flexible.
2. Description of the Prior Art
A wide variety of thermosetting compositions, each having various advantages and disadvantages, are known to this art.
Thermosetting compositions prepared from bismaleimides and hydroxylated silanes, for example, are described in French Pat. No. 2,460,308. These compositions do not have sufficient flexibility for certain intended applications. Furthermore, they display no adhesiveness in thin layer form.
Published French Patent Application No. 83/17,218 describes storage-stable compositions which are film-forming at temperatures of from 40.degree. to 90.degree. C. and preferably from 60.degree. to 80.degree. C., adhesive at ambient temperature and also flexible.
As utilized herein, by a "storage-stable" composition there is intended a composition which remains homogeneous (absence of crystallization of a constituent) and which does not change with time.
Also as utilized herein, by a "film-forming" composition there is intended a composition which is fluid at from 40.degree. to 90.degree. C. and may be deposited by spreading, or another conventional coating technique, onto a textile or a non-woven fabric, a fiber mat or a transfer paper, the fibers forming these various substrates being covered continuously, either directly or after transfer.
And by a composition which is "adhesive" at ambient temperature there is intended a composition which, when deposited onto a substrate and its temperature returned to ambient, the substrate can be positioned by mere pressure and will remain adhered in any position.
By a "flexible" composition there is intended a composition which, when deposited onto a substrate, does not increase the stiffness of the said substrate, enabling the latter to match the shapes of the parts to be produced therefrom which may be, for example, paths of revolution incorporating convex and concave sections and having rounded portions and/or ridges.
The aforenoted French Patent Application No. 83/17,218 more particularly relates to thermosetting compositions consisting essentially of:
(A) a prepolymer obtained by interreacting, at a temperature of from 50.degree. C. to 300.degree. C.:
(a) a bisimide or a combination of several bisimides, or a combination of a bisimide and N-cyclohexylmaleimide, said bisimide(s) being selected from among those of formula (1): ##STR1## wherein Y denotes H or CH.sub.3 and the symbol L denotes a divalent radical selected from among cyclohexylene, phenylene, 4-methyl-1,3-phenylene, 2-methyl-1,3-phenylene, 5-methyl-1,3-phenylene, 2,5-diethyl-3-methyl-1,4-phenylene radicals, and radicals of the formula: ##STR2## in which T denotes a group: ##STR3## and X denotes a hydrogen atom, a methyl, ethyl or isopropyl radical;
(b) an organosilicon compound incorporating, per molecule, at least one hydroxyl group bonded to a silicon atom;
(B) a triallyl isocyanurate or
an acrylic ester of a diphenylated siloxane compound having the general formula (4): ##STR4## wherein R is a hydrogen atom or a methyl or ethyl radical; and
(C) an imidazole compound.
Certain compositions have now been found, the properties of which are even more improved vis-a-vis those compositions described in said French Patent Application No. 83/17,218.